Powered roller conveyors are widely used in various manufacturing and transfer operations to permit goods to be transported to and between various locations, with the goods being handled on a "first in-first out" basis. One conventional conveyor as utilized with small or lightweight articles (i.e., less han 50 pounds) permits the articles to accumulate one after the other at the output end of the conveyor, with the accumulated articles abutting one another and slipping on the continuously driven conveyor rolls. This conveyor performs satisfactorily when dealing with articles of light weight since the driving force imposed on each article is hence of small magnitude, so that the line pressure which exists between adjacent articles and which accumulates along the row of accumulated articles remains rather small.
However, when dealing with heavy articles, particularly articles in excess of 500 or more pounds, such as engine blocks, then the driving force applied to each article is of much greater magnitude, and hence the accumulated line pressure which exists on and is exerted through the row of accumulated articles becomes of large magnitude. This is undesirable since it results in an excessive force being imposed on the stop located at the end of the conveyor, and hence severely restricts the number of articles which can be accumulated within a single row. For this reason, most powered roller conveyors when designed for use with heavier articles have necessarily involved the well-known and extensively utilized concept of "zoning." Such conveyor is divided longitudinally into a plurality of zones each having a preselected number of drive rolls associated therewith, and a suitable retractable stop is located at the discharge end of each zone. A control system involving switches and sensors is provided for interconnecting the various zones so that articles will be permitted to advance from one zone to the next only when the respective sensor indicates an opening in such zone. In this manner, the number of articles within each zone can be limited to a small number and hence the maximum accumulated line pressure can be limited to tolerable levels. Alternately, only a single article is accumulated within each zone so that zero line pressure exists along the conveyor between adjacent articles. These zoned conveyors, however, are necessarily complex both structurally and operationally due to the large number of zones required and the clutches and related control elements associated with each zone in order to disrupt the drive torque used for rotatably driving the rollers of each zone, and/or the provision of a separate drive for each zone, thereby making the conveyor expensive to construct and install, increasing the required maintenance, and requiring continuous and repetitive adjustmets of the system.
The present invention accordingly relates to an improved powered roller conveyor which can successfully transport, handle and stop heavy articles while resulting in the development of extremely small line pressure per article, specifically zero line pressure, whereby substantial numbers of such articles can be successfully handled and transported.
The improved conveyor of this invention, while providing zoning, nevertheless permits substantial simplification of the overall conveyor in contrast to prior systems in that it does not require special gear ratios or drives for creating a gap between articles when an article is advanced from one zone to the next, structurally and functionally complex drive disengaging devices such as clutches and the like associated with each zone for permitting disruption of the drive train, or separate drive motors and systems for each zone.
The improved roller conveyor of this invention successfully handles and transports heavy articles while permitting continuous and positive (i.e., nonslip) driving of the conveyor drive rollers or shafts. This conveyor is thus usable in situations wherein intermittent driving of the rollers or shafts was previously required, which intermittent driving required complex drive arrangements employing clutches and the like associated with each zone. In this invention, all of the support or drive shafts throughout the conveyor are positively and continuously driven by a single drive train from a single drive source, although selected conveyor rolls can be easily drivingly disengaged and stopped for zoning, or at a selected work station, while avoiding or minimizing the development of line pressure on the stopped articles.
In the improved conveyor of this invention, a plurality of conveyor rolls are formed as elongated sleeves and are freely rotatably supported on support shafts which are slightly undersized relative to the sleeves. At least selected support shafts at preselected intervals longitudinally along the conveyor are rotatably driven to thereby rotatably drive the conveyor rolls. The conveyor is provided with one or more zones, each having a plurality of conveyor rolls associated therewith. A lifting structure is associated with and extends longitudinally along the zone, being disposed below the conveyor rolls. Responsive to a signal, the lifting structure is moved upwardly a small distance, as by pressurization of an inflatable device, which lifting structure engages and slightly lifts the conveyor rolls sufficiently to effectively frictionally disengage them from the support shafts to thereby stop the roll rotation and hence stop the conveying of the article. This stoppage of the article occurs in a simple and efficient manner, while at the same time the support shafts associated with the zone are continuously and positively rotatably driven. All of the support shafts throughout all of the zones, and in fact throughout the complete conveyor, can be continuously and positively driven by a drive train of minimum structural and mechanical complexity, thereby permitting economical and dependable conveyor operation, even when handling extremely heavy loads.
Accordingly, it is an object of this invention to provide an improved conveyor with one or more article-stoppage zones, with each zone having an individual drive disengaging device associated therewith which permits limited lifting of the conveyor rolls from the support shafts to effectively disengage and hence stop the conveyor rolls and the article supported thereon. At the same time, the drive rollers or shafts as associated with the remainder of the conveyor can be continuously and positively driven at all times so that a greatly simplified and yet positive driving of the individual support shafts is possible.